In recent years, small, box-like, relatively flat cathode ray tubes in which the electron beam is generated parallel to the direction of the screen have become known. For instance, such tubes may be used in miniature or pocket televisions recently marketed.
Such a tube is disclosed in Sinclair U.S. Pat. No. 4,205,252 which is incorporated herein by reference. After being generated parallel to the screen, the electron beam is deflected electrostatically, and curved into the screen by a repeller electrode which is maintained at a negative potential in relation to the screen. The effect of the bending of the electron beam is that a raster having a keystone shape instead of the desired rectangular shape is scanned on the screen.
A prior art technique of compensating for the keystone distortion is to excite the deflection means with a complex electrical signal. However, such signals are relatively difficult and expensive to generate.